Mych as I love dogs, I cannot blame this man, I would have done the same, only my knives would not have bent, and bullets would have been involved.
As far as the human owner of this beast is concerned, I would like to think that I would have been able to control myself, but he deserves to be in jail for harboring a vicious animal, and he should be sued civilly.
True story: When my son was small, maybe 5, I was in the yard and saw him running down the street toward home and there was a big dog after him. I started running toward the dog and I really was going to kill it with my hands - there was no question I was going to do that. The dog saw me running toward him, turned around and took off. HE knew I was going to kill him.
I know that is what happened with this owner whose dog was going to die unless he did something fast. Something clicks in your head and you turn into a killer in an instant. I've been there and I was an instant killer with that dog after my child.